1. Field of the Invention
The present invention relates to a digital copier or multiple-function image processing device. The invention is more particularly related to the arrangement of the memory within the digital copier or multiple-function image processing device.
2. Discussion of the Background
Digital copiers are image processing devices which scan an image, store a digital representation of the image in memory, and print the digital representation of the image. In order to print the digitized images at a rate similar to rates produced by conventional analog copiers which never store a digital representation of the image but use optical components such as mirrors and lenses to generate an image on a photoconductive drum or belt, a very large amount of data must be moved at a high rate of speed. The requirement to quickly move such a large amount of data has pushed the capabilities of current data processing and storage devices to their limits.
Conventional digital copiers utilize separate memory systems for storing computer instructions and image data. This results in an isolation of the image data from the controller's main memory in which code (computer instructions) and data are stored for the controller's CPU. This is usually so because the rate at which image data must be accessed by the interface hardware is very high. These separate memory systems include separate semiconductor-based memory such as DRAMs for storing the instructions for controlling the processor of the digital copier and for storing images to be printed and images which result from a scanning operation. The separate memory systems also require separate memory controllers.
FIG. 25 illustrates the architecture of a conventional digital copier in which there are two separate memories; one for storing image or video data and the other for storing computer instructions and data relating to the operation of the system. A CPU 502 is connected to a ROM 504, a RAM 506, and a I/O port 508. While not illustrated in FIG. 25, a separate memory controller is needed to interface the ROM 504 and the RAM 506 to the CPU 502. The I/O port 508 is illustrated as interfacing to a scanner system and plotter system, although the scanner system and plotter system may each have their own I/O port. The I/O port 508 is utilized to control a scanner 510 and its mechanical components 512 which implement the scanning operation. The I/O port 508 also controls the operation of the plotter 518 along with its mechanical components 520 which are utilized to generate an image. Image data from the scanner 510 is transferred to the video memory 516 for storage through a memory controller 514. The stored image or video data within the video memory 516 is ultimately transferred to the plotter 518 for printing. While such a system provides for a very fast transfer of image data, it makes the system require the use of two memory controllers and also separate memories for the image or video data and for storing computer instructions or code, and the data or parameters associated therewith.
A digital copier having separate memory systems for the computer instructions and image data is somewhat limited in that if more memory is needed for storing computer instructions, spare memory which may exist for storing image data cannot be utilized. Similarly, if additional memory is desired to be utilized to store image data, if there exists spare memory or additional memory locations in the memory for storing computer instructions, this spare memory cannot be utilized to store the image data. Further, increased functions or image quality may require a large amount of memory for images. Even though spare memory may exist from the memory used for the controller or CPU, this memory cannot be utilized to store image data in conventional systems.
Additionally, as time progresses, the size of the memories which are being manufactured becomes larger and larger. For example, today, popular and inexpensive sizes of SIMMs (Single In-line Memory Modules) are around 16 and 32 megabytes. However, the size of the computer instructions utilized to control the digital copier may be one or two megabytes, or even less. Thus, smaller size inexpensive memories may be now or may in the future be hard to obtain.
Still further, if the digital copier or multi-function device is desired to be upgraded and perform additional functions or have additional capabilities, there may be a desire to increase the size of the memory which stores the computer instructions. However, in conventional systems with a memory system dedicated to storing computer instructions, it may become necessary to replace the memory used in the memory system for storing computer instructions with a larger size memory.